Conventionally, when performing hole-machining on a workpiece with a thin-wire bar-shaped or pipe-shaped electrode, what can be formed is only a straight hole having approximately the same hole diameters on both an upper surface and a lower surface of the workpiece, or a tapered hole having a larger hole diameter on the upper surface than that on the lower surface. As an electric discharge machining apparatus that forms a conical inverse-tapered hole having a larger hole diameter on a lower surface than that on an upper surface of a workpiece, there has been proposed an electric discharge machining apparatus that forms with a rod-shaped electrode on a workpiece a conical inverse-tapered hole having a larger hole diameter on a lower surface than that on an upper surface of the workpiece, where the machine includes a roller that feeds the electrode downward to stretch a lower part of the electrode to the workpiece, a lower guide that is arranged near the upper surface of the workpiece and is provided with a guide hole through which the electrode is penetrated, an upper guide that is arranged between the lower guide and the roller and is provided with a guide hole through which the electrode is penetrated, and a magnetic field positioned between the lower guide and the upper guide and directed to a direction perpendicular to the electrode formed by a magnet, thereby forming an inverse-tapered hole on the workpiece by rotating a free end of the electrode by passing a current changing along a time to the electrode and by causing the electrode to work rotating Lorentz force by rotating the magnetic field (for example, see Patent Document 1).    Patent Document 1: Japanese Patent Application Laid-open No. 2007-2263114 (Page 6, FIG. 2)